July 25, 2021

I, Science

The science magazine of Imperial College

Separating fact from fiction – everything you need to know about Zika virus.

virus and blood cellsOn February 1st 2016, the World Health Organisation (WHO) released a state of public health emergency of international concern (PHEIC), declaring the Zika virus to be the latest threat to global safety. Here, we separate fact from fiction and bring you the key information about this little known disease.

Where did the disease come from?

The scientific community has known about the Zika virus for almost 70 years. It was first identified near the Zika forest in Uganda, where it got its name.  Initially, it was thought the virus was confined to Africa, transmitted exclusively through mosquito bites. As such, there was thought to be little risk of a global epidemic; in 2007, the Centre for Disease Control and Prevention (CDC) stated that “fortunately, [Zika virus] illness to date has been mild and self limited”.  However increasing evidence shows that it can be transferred through person-to-person contact, including being found in sperm for up to three months after infection. To date, Zika virus has been found in 28 countries, but it is probable that it exists undetected in many more.

map of world with parts of south and central america highlighted in purple to indicate Zika transmission locations
Areas of reported active transmission of Zika virus taken from www.cdc.gov

So why are we only hearing about it now?

Because a Zika virus infection is not life-threatening. Only 20% of those infected develop symptoms, and the recover within a week without any apparent problems. However there is increasing suspicion of a link between the Zika virus and the rise in the number of babies being born with microcephaly.

What is microcephaly?

Microcephaly is a rare condition where a baby is born with a head that is considerably smaller than it should be. This is usually linked with the child having a small brain and abnormal brain function as well as a reduced life span.

How significant is the link between microcephaly and Zika Virus?

In July 2015, there was an outbreak of Zika virus in Brazil. The following September, a perceived increase in the number of births of microcephalic children was reported to the CDC. There had previously been reports that Zika virus can reach the brain of a child in the mother’s womb, so the researchers immediately started to investigate whether there was a link. In their investigation, the CDC found that within 35 mothers who had given birth to microcephalic children in that period, all had visited the Zika virus region.

The PHEIC is essentially based on this report. However, it is important to note that there is a colossal limit to this study: it is possible that there has not been an outbreak of microcephaly at all.

In their report, CDC researchers state that it is plausible that the number of children with mild microcephaly could have been underestimated before their study, and that the increase is due to a more precise diagnosis of the very mild cases of microcephaly. These could have gone undetected beforehand.

It is therefore possible that Zika virus has nothing to of with the development of microcephaly.

Then why did the WHO issue a warning?

view of Rio de Janeiro from a mountaintopIt is a precautionary measure while the scientific community investigate the connection between the virus and microcephaly. The PHEIC simply prompts travellers and people living in an area where Zika virus is present to protect themselves against infection. The emergency committee who advised the WHO in the run up to the PHEIC explain their decision in a letter to the reputable medical journal The Lancetin which they state “our advice […] was not made on the basis of what is currently known about Zika virus infection, […] it was rather made on the basis of what is not known about the clusters of microcephaly.

Is there a treatment?

As it’s name indicates, the Zika virus is a virus. Unlike bacteria, which can be treated with antibiotics, we do not have any all-encompassing medication against viruses. In some cases, scientists find a cure specifically tailored to one virus, like antiretrovirals for HIV. The other alternative is to develop a vaccine, however, it would need to be developed for each individual virus. The problem is that because Zika was considered to be relatively harmless, not much money has been put into researching how to counteract it. So for the time being, authorities recommend prevention.

Should I be worried?

While it is possible that Zika virus causes microcephaly, to this day there is no conclusive evidence that it does. Until science can prove this to be the case, the best policy is simply to follow the WHO’s recommendations and exercise caution as you would with any other viral infection.

Where can I get more information?

For further information, you can take a look at these websites:

Map of countries where Zika has been evidenced: http://ais.paho.org/phip/viz/ed_zika_countrymap.asp

Case study suggesting person-to-person contact: http://wwwnc.cdc.gov/eid/article/17/5/10-1939_article

2007 CDC report on Zika virus: http://wwwnc.cdc.gov/eid/article/15/9/09-0442_article

News article on links between Zika virus and neurological disorder GBS: http://www.isciencemag.co.uk/news/scientists-find-link-between-zika-virus-and-neurological-disease/

Marianne Guenot is studying for an MSc in Science Communication.

Images: Zika virus, Kateryna Kon; map of active transmission areas www.cdc.gov; Rio de Janeiro, Brazil, Caterina Belova.